Division of Health and Sport Education, United Graduate School of Education, Tokyo Gakugei University, Chiba, Japan.
Eur J Neurosci. 2009 Oct;30(7):1297-305. doi: 10.1111/j.1460-9568.2009.06895.x. Epub 2009 Sep 21.
Stretch reflexes and motor-evoked potentials (MEPs) of a muscle are facilitated when performing intensive contraction of muscles located in a different segment (remote effect). We investigated to what extent the remote effect on MEPs in the flexor carpi radialis (FCR) in humans is modulated during sustained maximal and submaximal voluntary contractions of the ipsilateral quadriceps (remote muscle). We found that even when the force of maximal voluntary contraction (MVC) of the remote muscle declined during sustained MVC, the magnitude of the remote effect on MEPs remained constant. Maximal electrical stimulation of the remote muscle and transcranial magnetic stimulation of the corresponding motor cortex revealed that the level of voluntary activation gradually decreased during the sustained MVC. The motor response in the FCR following magnetic stimulation at the level of the foramen magnum, which preferentially elicits muscle response as a direct response of the corticospinal tract, was not modified by the remote effect during the sustained MVC. This finding suggested that the excitability of the spinal motoneuron pool remained constant. In contrast to the sustained MVC, during sustained submaximal contraction of the remote muscle, the magnitude of the remote effect on MEPs gradually increased as muscle fatigue developed. These findings suggest that the remote effect on MEPs was dependent on the level of effort driving the remote muscle, but not on the actual level of force output of the remote muscle, and that the origin of the remote effect was supraspinal, putatively upstream of the primary motor cortex.
当进行位于不同节段的肌肉的强烈收缩时，肌肉的牵张反射和运动诱发电位（MEPs）会被促进（远程效应）。我们研究了在对侧股四头肌（远程肌肉）进行持续最大和次最大自主收缩期间，这种对人类桡侧腕屈肌（FCR）的 MEPs 的远程效应在多大程度上被调节。我们发现，即使远程肌肉的最大自主收缩（MVC）的力在持续 MVC 期间下降，MEPs 的远程效应的幅度仍保持不变。对远程肌肉进行最大电刺激和对相应运动皮层进行经颅磁刺激表明，在持续 MVC 期间，自愿激活水平逐渐降低。在经颅磁刺激时，在枕骨大孔水平下，运动反应优先作为皮质脊髓束的直接反应而引起肌肉反应，在持续 MVC 期间不受远程效应的影响。这一发现表明脊髓运动神经元池的兴奋性保持不变。与持续 MVC 相反，在持续的远程肌肉次最大收缩期间，随着肌肉疲劳的发展，MEPs 的远程效应的幅度逐渐增加。这些发现表明，MEPs 的远程效应取决于驱动远程肌肉的努力水平，而不是远程肌肉的实际力输出水平，并且远程效应的起源是脊髓上的，可能在上运动皮层之前。
